CVE-2021-42125

What it actually does

The vulnerability is an unrestricted file upload flaw in Ivanti Avalanche prior to 6.3.3 affecting the Inforail Service. A low-privileged attacker with network access to the service can upload files without sufficient validation of file type, content, path, or execution risk. If the uploaded file is placed in an executable or service-accessible location, this can lead to arbitrary file write, remote code execution, data access, service tampering, or denial of service. The CVSS 8.8 rating reflects low attack complexity, no user interaction, and high confidentiality, integrity, and availability impact after authenticated access.

Why it matters to the business

Successful exploitation can allow an attacker to take control of systems running the vulnerable service, disrupt device-management operations, alter managed-device configuration, steal sensitive operational data, or use the server as a foothold for broader internal compromise. Although this is not listed in CISA KEV and no ransomware association is provided, the EPSS score is high, indicating meaningful likelihood of exploitation activity; the issue is also long-published, so unpatched internet- or partner-accessible instances should be treated as high-priority exposure.

How an attack unfolds

An attacker first obtains valid low-privileged access to the Inforail Service or reaches an interface that accepts authenticated file uploads. They then submit a crafted upload request containing a dangerous file type, such as a script, web shell, executable payload, or configuration file intended to alter service behavior. Because vulnerable versions do not adequately restrict uploaded content or destination, the service writes the attacker-controlled file to disk. The attacker then attempts to trigger the uploaded file directly through the application, wait for the service to load it, or use the file write to overwrite or plant content that is executed by another component. Once code execution or control is achieved, the attacker can establish persistence, collect credentials or application data, pivot to adjacent systems, and interfere with availability of the Avalanche management service.

How to fix it

Upgrade Ivanti Avalanche to version 6.3.3 or later. If tracking source-level remediation from the supplied package metadata, ensure rancher-sandbox/rancher-desktop builds include commit 97d211bc11adb8ad281ef792d8bbc58b56c7123b; however, validate product applicability because the vulnerability description identifies Ivanti Avalanche/Infrorail Service as the affected technology. Until upgraded, restrict network access to the Inforail Service to trusted administrative networks, require strong authentication, disable or limit upload functionality where operationally possible, block uploads of executable or scriptable file types, enforce server-side allowlists for extensions and MIME types, store uploads outside executable paths, and monitor for newly created unexpected files under application directories.

How to confirm the fix worked

Confirm the installed Ivanti Avalanche version is 6.3.3 or later, or verify the relevant build contains the fixed commit 97d211bc11adb8ad281ef792d8bbc58b56c7123b where that package metadata is applicable. Review service exposure to ensure the Inforail Service is not accessible from untrusted networks. Test upload controls in a non-production environment by attempting to upload benign files with executable extensions and confirming they are rejected, renamed safely, stored outside executable directories, and never directly executable. Review file-system permissions to ensure the service account cannot write to web roots, binary directories, startup paths, plugin directories, or other execution-sensitive locations.

Typical attack path

1. Identify an exposed or reachable Ivanti Avalanche Inforail Service instance.
2. Authenticate with low-privileged credentials or otherwise gain access to upload functionality.
3. Send a crafted file upload request containing executable, scriptable, or service-impacting content.
4. Abuse insufficient validation to write the file to a dangerous location on the server.
5. Trigger execution or service processing of the uploaded file, or use the file write to alter application behavior.
6. Escalate post-exploitation activity by collecting data, adding persistence, modifying managed-device configurations, or moving laterally.

How to detect it

Investigate whether exploitation already occurred by reviewing Inforail Service and Ivanti Avalanche application logs for authenticated upload activity, failed or unusual upload attempts, unexpected file names or extensions, and requests followed by server errors or new process execution. Correlate web or service access logs with file-system timeline data to identify files created by the service account in application, upload, temporary, plugin, web-accessible, binary, or startup directories. Examine endpoint telemetry for the Inforail Service spawning shells, scripting interpreters, archive tools, download utilities, or network tools. Review authentication logs for low-privileged accounts accessing upload functionality from unusual IP addresses, at unusual times, or immediately before new files appeared. If suspicious files are found, preserve them for malware analysis, collect hashes, inspect contents for web-shell behavior or command execution logic, and determine whether credentials, device-management data, or configuration files were accessed after the upload.

• Inforail Service
• multipart/form-data
• .jsp
• .war
• .aspx
• .php
• .exe
• .dll
• .bat
• .cmd
• .ps1
• cmd.exe
• powershell.exe
• /bin/sh
• /bin/bash

What your security team should do

• Prioritize patching or compensating controls for any reachable Ivanti Avalanche instances running versions earlier than 6.3.3, especially those exposed beyond a tightly controlled management network.
• Inventory all systems running the Inforail Service and verify version, network exposure, authentication requirements, and upload functionality.
• Restrict access to the service using firewall rules, VPN, administrative jump hosts, and allowlisted source ranges.
• Hunt for suspicious uploaded files, especially recently created executable or script files in Avalanche application, web, service, plugin, temporary, or upload directories.
• Review authentication logs for unusual low-privileged account activity followed by file upload events or service errors.
• Add detection coverage for unexpected file creation by the Inforail Service process and for child processes spawned by the service.
• Rotate credentials and review privileged accounts if evidence suggests suspicious uploads or code execution occurred.